The earliest shrimp farms consisted of near shore impoundments to which small numbers (1-3 shrimp/m.sup.2) of wild caught shrimp postlarvae (wild seed) were stocked. Several hundred kilograms/hectare of adult shrimp were harvested periodically. These farms in essence practiced natural balanced ecosystem growout; no feed was added to the growth medium, no water was exchanged, no aeration or mixing was performed, and no water treatment was provided.
Most shrimp farm operations have retained dependence upon wild seed, but have raised stocking densities. Yields of 1,000-3,000 g/m.sup.2 became standard, and some farm operations reported yields of 10,000 g/m.sup.2. Some prerequisites to these higher yields were substantial modifications in farm management practices including but not limited to use and dependence upon supplemental feeds such as trash fish, manufactured feed or both; water exchange; and aeration/mixing. Generally the higher the stocking density, the more the farming system depended upon quality high protein and high energy feeds, water exchange, and aeration/mixing.
Currently, the impact and spread of shrimp diseases and mortality rates of shrimp are the dominant concerns of shrimp farmers around the world. Pathogenic viruses and other disease agents for shrimp are commonly found in wild shrimp populations and in river and coastal waters where shrimp or other crustaceans are or may be farmed. These pathogens are also carried by workers, birds, and wind, and may contaminate the shrimp population, with devastating results on crop growth and yield.
Thus, there is a need for an economical system or method for intensive production of high quality disease free marine animals which minimizes environmental side effects.
Development in the area of zero-exchange systems has led to significant changes in the art of aquaculture. For example, Fahs et al., U.S. Pat. No. 5,353,745, disclosed an apparatus and method for maintaining aquatic organisms in an essentially closed system, wherein the aqueous medium is removed from the tank, sterilized, and returned following purification and removal of solids produced in the system. Further, Lee et al., U.S. Pat. No. 5,961,831, disclosed a similar closed aquaculture system with automated water purification. Both of these inventions provide systems for the growth of commercially desired marine animals with near zero water replenishment. However, these systems utilize only "clean water" or "clean conditions" within the system. Therefore, these systems are not true zero-exchange systems as defined below because in the above noted systems, solids introduced into the system (typically feed) and produced within the system (typically fecal matter and metabolites) are continuously removed from the system along with recycled aqueous medium.
It is because solids are removed from the above systems that the systems fail to recognize the importance of maintaining solid residues, fecal matter, particulate matter, metabolites, and uneaten feed in an intensive zero-exchange growout system to provide an environment favorable for high growth rates and yields of shrimp and certain marine animals. "Clean water" systems do not establish these favorable conditions for intensive growth and harvesting of marine animals, specifically at levels of up to 10,000 kilograms per hectare. In the instant invention, adapting both the nutrition source and the mixing/aeration ratio compensates for any unfavorable changes in the system and maintains the favorable conditions throughout the growth cycle, whereas the industry has heretofore utilized filtering, flushing, or removing contaminants from the aqueous medium as the primary mechanism for controlling aqueous medium quality.